The research proposed in this application is carried out with the objective of obtaining basic information which can be used to build an understanding, in molecular terms, of physiologically important biological membrane phenomena. Work is centered on the continuing investigation of the interactions between lipids in multicomponent bilayers and between lipid and protein components in these systems. Of special interest are multicomponent bilayers exhibiting compositional domain structure either within the plane of the bilayer or between its apposing faces. The research is specifically aimed at answering the following questions. a) What are the physical and biologically relevant properties of multicomponent bilayers with in-plan compositional domains? b) What are the physical and biologically relevant properties of multicomponent bilayers with different compositions in the two constituent monolayers? c) What are the thermodynamic and kinetic parameters governing the insertion of hydrophobic peptides into multicomponent bilayers as assessed by bilayer interaction with semi-synthetic proteins formed from hydrophobic peptides linked to bovine pancreatic trypsin inhibitor? The bilayer systems employed in this study are primarily unilamellar vesicles with radii greater than 400A and planar oriented multibilayers. Glycerol-based lipids are of central concern. Interactant proteins are formed by linking synthetic hydrophobic peptides to a carrier protein, bovine pancreatic trypsin inhibitor. Assessment of the parameters governing interactions between components and the properties of compositional domain systems will depend upon a variety of physical techniques. These include the use of fluorescent probes, NMR spectroscopy (1H, 2H, 13C, and 31P), ESR spectroscopy, differential scanning calorimetry and the use of hydrodynamic and equilibrium methods to characterize vesicle dispersions. The studies outlined in this proposal depend critically not only on physical techniques but also on analytical techniques long in use in this laboratory and on the established capacity of the laboratory to synthesize, prepare from natural sources, and modify chemically a wide variety of membrane lipids.